In this nonrandomized phase I/II study, a maximum of 20 HIV-infected patients with toxoplasmosis who have failed standard therapy or who cannot tolerate standard therapy will be treated with the combination of pyrimethamine and dapsone. Toxicity and efficacy will be assessed. The starting doses will be pyrimethamine 25 mg/d and dapsone 100 mg/d with folinic acid 10 mg/d; dose modifications include increasing the dapsone and pyrimethamine dose in patients failing the lower dose, and increasing the folinic acid dose and decreasing the dapsone and pyrimethamine dose in patients manifesting toxicity from the combination. Patients responding clinically or radiographically can continue therapy indefinitely as tolerated to prevent relapses because there are no other approved therapies tolerated by these patients for this life-threatening infection. This study assesses an alternative to sulfadiazine-pyrimethamine for therapy of toxoplasmosis: such an alternative is important because so many patients cannot tolerate sulfonamides.